World Cup: Can Cristiano Ronaldo Shake His Knee Injury?

The world player of the year hasn't been able to shake a lingering left knee injury since coming to Brazil, but he trained normally Saturday and is expected to start Sunday when the Portuguese face the United States in a crucial Group G match at the World Cup.

"He trains everyday with all of us. So Cristiano is fit to play," Portugal midfielder Raul Meireles said Saturday. "That's all I can say."

Ronaldo took the field with the rest of his teammates and did several running drills, not appearing to be affected by the injury. He did, however, again have some wrapping below his left knee.

Portugal lost its opening match to Germany 4-0, and another loss on Sunday will mean immediate elimination from the World Cup. The Americans, however, won their opening game and can secure a spot in the second round with another victory.

As usual when Ronaldo plays, though, the outcome of the match can be easily swayed by a moment of brilliance from the Real Madrid winger.

"He's strong physically. He's a fast runner. He's the best in the world with the ball at his feet," United States goalkeeper Tim Howard said. "That's why he's the best player in the world.

"We're going to do our best to bottle him up."

Ronaldo played in the loss to Germany on Monday, but he has since been seen at training with a brace on his left knee.

If he is not 100 percent healthy for the match at the Arena da Amazonia, an already undermanned Portugal could struggle to earn the three points needed to stay in the tournament.

Portugal coach Paulo Bento, however, said he is not putting any pressure on his star player.

"In October 2010, I told him once and that's it, I would never put on his shoulders, or anybody else, the responsibility to solve the problems," Bento said. "The only person that has one individual responsibility is me."

Even with Ronaldo on the field, Portugal will be short-handed.

Defender Fabio Coentrao, Ronaldo's teammate at Real Madrid, and striker Hugo Almeida have been ruled out of the rest of the World Cup with injuries. Pepe, another Real Madrid defender, is suspended.

The shakeup on the field won't be the only changes in the Portugal team following the opening loss.

"We have to change the result," Meireles said. "It's not because of a defeat in the previous game that we're going to change. We all know what we have to do. We're all prepared to do our best."

The match will be the third to be played in the heat and humidity at the Arena da Amazonia in Manaus, the most exotic of the 12 World Cup venues.

Both sides say they are prepared for the conditions.

"Everybody can feel the difficulty that we and the United States will have tomorrow. Very high humidity," Meireles said. "That is a complicating factor, but it's complicated for both teams, so we can't have any excuses there."

Whether it's the weather, the injuries or anything else, the certainty for Portugal is the need for victory on Sunday.